On Sat, 16 Apr 2011 15:44:58 -0500, Vic Smith
wrote:

On Sat, 16 Apr 2011 13:23:29 -0400, "Wilbur Hubbard"
wrote:



An ignorant bit of advice, as usual, Bruce. What if the system has a small
leak. Then all the vacuum pump will accomplish is to suck humid air through
the system. If you're going to use a vacuum pump you can't go home and have
a beer and ignore the readings. If it won't hold a hard vacuum then you got
problems. Using dry nitrogen to pressurize the system before vacuuming it
out absorbs any moisture that might have gotten into the works. Try reading
the article. Oh, that's right, you are functionally illiterate. Never mind!


I've vacuumed a number of A/C systems. Have a pretty good pump, rated
about 200 microns.
Standard practice is to pump down to the pump's rating, then turn off
the pump, isolate it with the gage set valve, and wait a while to see
if there's any leakdown on the gage.
I usually give it 5 or 6 hours to feel confident there's no leak.
But you're vacuuming because you've had a leak or failed component
and fixed that.
You're just verifying there's no leak before filling.
The main purpose of vacuuming is to eliminate moisture.
You'll know you have a leak if the gage changes, but not where.
Then you bring out the dye to find the leak, fix it, and vacuum again.
There's no worry about sucking in humid air if you fix it.
In the end the system will be dry before you add refrigerant.
Any time you remove an A/C component the system fills with humid air
anyway.
Not ideal, but before I bought my 200 micron pump I replaced a couple
compressors without vacuuming at all and the systems ran fine for
years.

Also used air-driven pumps to vacuum with no issues.
Air-driven pumps probably won't go below 2000 microns, not nearly
enough to eliminate all moisture. Better than nothing though.
Anyway there's usually some leeway when you do this.
Now, you can get a 200 micron pump and a gage set for under $200,
so car and boat A/C can be DIY with a little study.
Not familiar with boat reefers, but they seem amenable to DIY with the
same equipment.

Only use of dry nitrogen pressurization with A/C I've seen is in
conjunction with a freon leak detector, flushing when going to a
different refrigerant, and some industrial A/C testing and
maintenance.
I googled that out of curiosity, because I hadn't heard of it..
I've always easily found A/C leaks using UV dye and a light.

--Vic

Forget the technical explanation. You are writing to a fool that knows
HE is right and that the rest of the world is wrong.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)